1. Field of the Invention
This invention relates to an open-celled sponge having a cellulosic component of large pore size and a polyvinylchloride component of small pore size.
2. Description of the Prior Art
In the field of pollution control, it is often sought to remove toxic organic substances from water. The organic substances may be present in dissolved or suspended form, and may be present in large amounts, or in small amounts such as in parts per million, parts per billion, or less. Exemplary toxic organic species include: polychlorinated biphenyls, dioxins, polyaromatic hydrocarbons, nitroaromatics, pesticides, herbicides, methyl t-butyl ether, and volatile halocarbons.
Current technology for removing such organic contaminants involves the use of activated carbon. However, the activated carbon, generally in granular form, must be confined within a vessel as a bed through which the water to be treated is caused to flow. The bed of carbon granules generally creates impedance to the water flow, requiring adequate pumping to achieve a sought flow rate. Also, suspended material in the in going water stream may accumulate within the bed to cause even higher flow impedance. Although activated carbon functions efficiently, its total capacity or absorbed species is low, often less than 2% of the weight of the carbon. This results in the need to handle large amounts of carbon for the removal of relatively small amounts of contaminants.
Another problem in the field of pollution control is filtration for the removal of extremely fine suspended particles. Classic filtration methods employ, for example, sand bed filters and plate and frame presses. Such equipment is of large size and considerable expense, and requires careful monitoring to assure proper performance. Filters involving a porous membrane are usually employed for removing small quantities of very fine particles that may have passed through conventional filters. The membrane filters, however, are easily clogged or "blinded" when relatively little material accumulates on the upstream surface of the membrane.
The use of a microporous form of polyvinyl chloride (PVC) in filtration applications has been disclosed in U.S. Pat. No. 3,674,722. Although the microporous PVC performs well in filtration applications, it is difficult to produce useful shaped structures from the microporous PVC because of shrinkage during molding. Also, such shaped structures have been found to be brittle. When the shaped structure involves a continuous smooth upstream filtration surface, the microporous PVC filter clogs as easily as less expensive membrane filters.
It is disclosed in said U.S. Pat. 3,674,722 at column 3, lines 41-42 that the microporous PVC can be inserted as an impregnant into porous structures such as open celled foams. It has been found however, that with most such foams, unless the PVC completely fills the pores, it tends to flake away from the foam. Such is particularly the case with rigid foams or sponges comprised of polyethylene, polyurethane, polystyrene, phenolics, metals, ceramics or glass. When the pores of the foam are completely filled with the PVC, the resultant composite structure develops a very high impedance to the passage of fluids therethrough. If the sponges become soft when immersed in water, their usefulness is diminished because of compressive effects encountered during water treatments.
It is accordingly an object of the present invention to provide a rigid sponge structure capable of absorbing organic pollutants from water.
It is another object of this invention to provide a sponge structure as in the foregoing object having relatively low impedance to the passage of fluids therethrough.
It is a further object of the present invention to provide a sponge structure of the aforesaid nature capable of filtering suspended particles out of water.
It is a still further object of this invention to provide a sponge structure of the aforesaid nature resistant to compression under hydraulic pressures encountered during water treatment.
It is yet another object of the present invention to provide a sponge structure of the aforesaid nature amenable to low cost manufacture.
These objects and other objects and advantages of the invention will be apparent from the following description.